DEVELOPMENT OF A TOTALLY COMPUTERIZED INTERACTIVE FATIGUE LIFE ANALYSIS PROGRAM

The most effective approach in fatigue analysis is to intimately involve the structural analysts in the selection and decision criteria for all of the elements of the analysis. Current fatigue life calculation systems incorporate computerized capability to deal with variations of any one or two of the three major parameters that are involved: (1) the usage spectrum, (2) the flight load levels, and (3) the fatigue strength allowable curve. In many applications, it is advantageous to quickly iterate many such calculations, varying spectrum, loading and strength variables. Current systems may require significant off-line activity to rework, for example, strength or flight load data, before returning to the primary analysis. The new MDHC advanced computer facilities provide a central location for storing large volumes of flight test data and S-N curve data. An interactive computer code has access to the flight data, and using statistical selection criteria, sums the damage for particular maneuvers, spectra of particular maneuvers or the entire usage spectrum. Furthermore, the code permits review of potential spectrum variations and allows rapid alterations. Simultaneous iterations of flight test data and S-N curve selection criteria are also permissible at the computer keyboard. Alternative S-N curve shapes, strength levels and scatter factors are immediately available through a built-in data base and cause-effect program. The development of these standards expedites the entire fatigue analysis procedure and enables the data to be presented in a more manageable and user-friendly format. Figures and tables are included demonstrating the actual formats and options.